feat(inventory): informal quantity scale (number + unit) + seed/plant lots

Rework quantities the way seeds are actually described — a number of an informal
unit — and let a lot hold seeds or plants (plantel).

Quantity model (commons_core):
- Quantity is now { kind, count?, label } — "3 cobs", "2 packets", "a few".
  Count is optional; uncountable vibes (a few, some, pinch) carry no number.
- QuantityKind reorganised into an ascending scale: vibes → containers
  (teaspoon/spoon/cup/jar/sack) → seed & fruit forms → plant units, each tagged
  countable/not. Stored by name; count reuses the existing numeric column.

Lot type (schema v2):
- Lots gain a `type` (seed | plant); germination stays meaningful for seeds.
  schemaVersion 2 with a from1To2 migration (adds the column), drift_schema_v2
  exported, migration test covers v1→v2.

UI:
- New QuantityPicker: a horizontal scale of large seed-glyph icons + a number
  stepper (shown only for countable units), plus a seed/plant SegmentedButton.
  Used in quick-add and add-lot. Lot lines render "3 cobs" / "a few".
- i18n: unit singular/plural (ES/EN, Weblate-friendly), lot-type labels.

Build: slang moved to its CLI (disabled in build_runner to avoid a multi-file
collision); CI runs `dart run slang` before build_runner. 38 tests green,
Linux migrates the existing v1 DB and runs.

apps/app_seeds/lib/ui/quick_add_sheet.dart

@@ -1,6 +1,5 @@
 import 'dart:typed_data';
 
-import 'package:commons_core/commons_core.dart';
 import 'package:flutter/material.dart';
 import 'package:flutter_bloc/flutter_bloc.dart';
 import 'package:image_picker/image_picker.dart';
@@ -8,24 +7,12 @@ import 'package:image_picker/image_picker.dart';
 import '../data/variety_repository.dart';
 import '../i18n/strings.g.dart';
 import '../state/quick_add_cubit.dart';
-import 'quantity_kind_l10n.dart';
-import 'seed_glyph.dart';
+import 'quantity_picker.dart';
 
 /// Picks a photo and returns its bytes (or null if cancelled). Injected so
 /// widget tests can supply a fake instead of the camera plugin.
 typedef PhotoPicker = Future<Uint8List?> Function();
 
-/// A short, high-frequency subset of quantity units shown up front to keep the
-/// add flow fast; the rest live behind "Add more…".
-const _quickKinds = <QuantityKind>[
-  QuantityKind.aFew,
-  QuantityKind.handful,
-  QuantityKind.packet,
-  QuantityKind.pod,
-  QuantityKind.cob,
-  QuantityKind.grams,
-];
-
 Future<void> showQuickAddSheet(
   BuildContext context, {
   required VarietyRepository repository,
@@ -94,22 +81,24 @@ class QuickAddSheet extends StatelessWidget {
                 onSubmitted: (_) => cubit.submit(),
               ),
               const SizedBox(height: 16),
+              LotTypeSelector(
+                value: state.lotType,
+                onChanged: (type) {
+                  cubit
+                    ..setLotType(type)
+                    ..setQuantity(null);
+                },
+              ),
+              const SizedBox(height: 12),
               Text(
                 t.quickAdd.quantity,
                 style: Theme.of(context).textTheme.labelLarge,
               ),
               const SizedBox(height: 8),
-              Wrap(
-                spacing: 8,
-                children: [
-                  for (final kind in _quickKinds)
-                    ChoiceChip(
-                      avatar: QuantityKindIcon(kind, size: 18),
-                      label: Text(quantityKindLabel(t, kind)),
-                      selected: state.quantityKind == kind,
-                      onSelected: (_) => cubit.selectQuantity(kind),
-                    ),
-                ],
+              QuantityPicker(
+                type: state.lotType,
+                value: state.quantity,
+                onChanged: cubit.setQuantity,
               ),
               const SizedBox(height: 8),
               Align(